2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
Many people today cannot believe that man - such, in essence, a fragile and ephemeral creature - has become a global force, a geological factor capable of changing the fate of the entire planet. In the middle of the 20th century, only philosophers talked about this, but several decades ago a number of discoveries were made that proved that mankind now lives in a new era, in which it itself acts on an equal footing with the forces of nature. However, there is no need to be proud of this - we make this planet less favorable for ourselves. One of those who spoke about the power of humanity and how it threatens us was the chemist Paul Krutzen, with whom we said goodbye this week.
Difficulties with ozone
By the late 1950s, there were no special mysteries associated with atmospheric ozone in science. The theory of the British Sidney Chapman, proposed back in 1930, was generally recognized at that time. He believed that the ozone layer is in a state of stable photochemical equilibrium. Ozone is constantly produced by the action of ultraviolet radiation from the Sun on molecular oxygen O2, and destruction occurs as a result of the recombination of atomic oxygen and ozone.
Everything changed in 1957, which was declared the International Geophysical Year. Scientists around the world have launched large research projects: for the geophysical year, for example, the launch of the first satellite was timed, and it was at this time that the first global network of ozonometric stations appeared. This network allowed for a much more accurate description of the spatial distribution of ozone - both horizontally and vertically.
And then it became clear that Chapman's theory corresponded to the data only in very general terms and did not help in any way to understand the numerous details and subtleties. Among them, for example, she could not explain the significant variations in ozone in cyclones, in the intertropical convergence zone, in jet streams. The theory of the influence of the hydrogen cycle was added to Chapman's theory, but it did not solve the problem - in it, ozone destruction was underestimated in the lower stratosphere and overestimated in the troposphere.
The person who was able to sort out these contradictions and uncertainties was Paul Krutzen, an engineer by training, who began working at Stockholm University in 1959, where he defended his Ph. D. thesis in 1968, and in 1973 - work for a doctorate degree (D. Sc.). Both dissertations and subsequent work of the 1970s-80s were devoted to atmospheric ozone. He investigated the catalytic cycle of the destruction of stratospheric ozone by nitrogen oxides and, in general, the role of nitrogen oxides in chemical processes in the atmosphere, the catalytic mechanism of ozone formation in the troposphere, and the processes of chlorine activation in the stratosphere over Antarctica.
He managed to remove the uncertainties of previous theories by showing that methane, nitrogen and chlorine compounds play a critical role in the global atmospheric ozone cycle. And already in those years he began to talk about the destructive role of the human factor. In particular, he was the first to assess the scale of the environmental threat associated with supersonic aircraft, which flew at altitudes of about 18 kilometers. By comparing the intensity of natural sources of nitrogen oxides in the stratosphere with emissions from such aircraft, Crutzen showed that the ozone layer would begin to degrade if only 500 supersonic aircraft were regularly flown.
In addition, Crutzen determined how ozone is formed in the lower atmosphere, where this gas is extremely toxic. He described the photochemical mechanism of ozone formation due to the catalytic cycle involving nitric oxide and oxidation products of methane and carbon monoxide, such as the peroxyl radical HO2 or CH3O2, and thus, in fact, developed the theoretical basis for taking measures to improve air quality in cities. This ultimately led to the phasing out of coal combustion in cities, and a switch to cleaner fuels for cars.
When, in 1985, British polar explorers discovered that ozone concentration dropped sharply over Antarctica in winter - the so-called "ozone hole" was formed, Crutzen was among the first to establish the mechanism that leads to its appearance. He showed that if, under normal conditions, chlorine and nitrogen oxides neutralize each other, then at an air temperature below 205 kelvin (under polar night conditions in the stratosphere over Antarctica), nitrogen from a gaseous state goes into a solid state and leaves the chemical cycle, which ultimately leads to to the rapid destruction of ozone by chlorine oxides.
The source of chlorine in the stratosphere, Crutzen called the decomposition of freons - chlorofluorocarbon compounds that were produced by industry in different countries and were used as refrigerants that entered the upper atmosphere and decomposed under the influence of solar radiation (in parallel, the same idea was expressed by Mario Molina and Sherwood Rowland, but there were also other theories, for example, the appearance of ozone holes were explained by the influence of volcanic eruptions).
Decreases in atmospheric ozone over Britain's Halley Station in Antarctica, and satellite ozone map as of 10 September 2000
It was for these studies that Crutzen, together with Molina and Rowland, received the 1995 Nobel Prize in Chemistry.
His work became the scientific basis for the Montreal Protocol on Substances that Deplete the Ozone Layer. What is noteworthy: this is also a rare case when the results of scientific work turned out to be a decisive factor that changed the policies of countries (and significantly influenced the global economy). True, given the extremely long life of freons, the positive effect of compliance with the protocol is very difficult to discern behind the dynamics of the stratosphere, which determines the main variability from year to year. Fortunately, humanity does not have to experience the negative effects of the lack of this protocol. For more information on the history of the Montreal Protocol, see The Hole We Can Fix.
It must be said that Crutzen was not only a theorist who generalizes and analyzes the data collected by others. He initiated a series of large projects to measure the state of the atmosphere in different regions of the Earth (here are just a few of them: INDOEX, CONCERT, MOZAIC, CARIBIC). One of the experiments - "railway" - he organized on the territory of Russia in the 1990s together with Academician Georgy Golitsyn and Professor Nikolai Elansky.
The TROICA project (TRanscontinental Observations Into the Chemistry of the Atmosphere) involved measuring the state of the atmosphere on the transcontinental railway routes of Russia: along the quasi-latitude section Moscow-Vladivostok and the quasi-meridional Murmansk-Kislovodsk (1, 2, 3, 4). The observations were carried out using a specially created "laboratory on wheels", consisting of two cars, which was able to carry out automated observations of more than 40 atmospheric gases, aerosols, radiation and meteorological characteristics. A total of 13 observation campaigns were carried out from 1995 to 2009.
Railway observatory car of the TROICA project
The studies have substantially supplemented the scant information on sources, effluents, transport and chemical transformations of atmospheric constituents in many regions of Northern Eurasia. Scientists have obtained accurate data on the differences in air quality in large Russian cities and background regions, once again assessing our impact on the world around us.
One of the results of the TROICA project: profile of the concentration of nitrogen oxide NO in Tyumen and the surrounding area
Nuclear winter and geoengineering
Since its inception, nuclear weapons have been considered an extremely dangerous military instrument, but only in the early 1980s, when the expression “nuclear winter” was expressed, it became clear that this is a means for collective suicide not only of humanity, but of practically the entire biosphere. Perhaps this understanding played an important role in the fact that a nuclear war did not happen then. Crutzen was one of those who began to assess the climatic consequences of a nuclear war. In his 1982 work The Atmosphere After a Nuclear War: Twilight at Noon, assessing the possible impact of nuclear exchange on the ozone layer in the stratosphere, he showed that a possible nuclear war would not be fatal for the ozone layer, but something else would happen as a result of the conflict. an important consequence is the strong aerosol cloudiness of the atmosphere.
Perhaps it was Krutzen who first spoke about this factor - even before the classic article on nuclear winter by Carl Sagan and co-authors came out. Krutzen's work gave rise to research, including Soviet climatologists Georgy Golitsyn and Alexander Ginzburg, Nikita Moiseev and Vladimir Alexandrov, who found out that this turbidity would lead to a sharp cooling - that is, "nuclear winter". Scientists have clearly demonstrated that not only one side (the loser) will suffer, but also the winner, and indeed everyone else who did not even participate in the war.
Later, Crutzen also turned to the topic of climate change, published a number of works devoted to the study of the role of aerosols in the earth's climate system (1, 2, 3). At the same time, he understood that it is extremely difficult to achieve a reduction in greenhouse gas emissions on a global scale and to mitigate the anthropogenic impact on the climate. And if in the case of the ban on ozone-depleting substances, the countries were able to agree, then the climate negotiations under the auspices of the UN are progressing with great creak - progress in this area is still very modest.
Realizing that political differences can only be overcome with great difficulty, in 2006 Krutzen turned to the idea of geoengineering, voiced by academician Mikhail Budyko in 1974 in the book "Climate Change" hands "). Like his predecessor, he proposed to purposefully influence the climate by creating a sulfate aerosol screen in the stratosphere, which would reflect part of the sunlight into space and thus lead to the cooling of the planet: that is, what in the event of a nuclear war would lead to disaster, here in small quantities could be useful.
Crutzen urged his colleagues to make careful calculations so that the scientific community would have an answer to the question, is it possible, effective, and most importantly, is such a "plan B" safe?
The advent of the Anthropocene
Realizing that human activity is not limited to the influence on the chemistry of the atmosphere, Krutzen formulates the idea of the Anthropocene - a new geological era, where the influence of human activity becomes one of the most important forces. The idea, based on the concepts of the noosphere by Vladimir Vernadsky and Teilhard de Chardin (whose influence is written by Krutzen himself), received wide publicity after articles in the IGBP Global Change Newsletter and in the journal Nature.
Crutzen cites four main "indicators" that speak of the arrival of a new geological age:
- it is the depletion of more than 40 percent of the known oil reserves, which took several hundred million years to build up;
- transformation of almost half of the land surface, which significantly affected biodiversity, the cycle of substances, soil, climate;
- fixation of nitrogen for fertilizers by volume now exceeds its fixation in natural ecosystems;
- more than half of the available fresh water is used for human needs, and groundwater resources are rapidly depleting.
Later, he adds to this list the increase in the concentration of greenhouse gases in the atmosphere and the destruction of tropical forests.
Although the International Commission on Stratigraphy and the International Union of Geological Sciences have not yet officially approved this term as recognized, it seems that it is only a matter of time. In addition, the boundaries of the beginning of the Anthropocene have not yet been precisely determined.
Back in 1992, Krutzen and Golitsyn expressed ideas about the limits of our impact on nature, in their work on the links between global warming, ozone depletion and other aspects of environmental change. And in 2009, Krutzen joined the group of scientists who formulated the concept of the so-called "planetary boundaries". Scientists have identified nine conditional systems (areas) of the environment (air pollution by aerosols, climate change, water resources, environmental management, ocean acidification, depletion of the ozone layer, biogeochemical cycles, loss of biodiversity, chemical pollution), in which safe limits for human activities should be set. The crossing of these limits, according to the authors, can lead to catastrophic consequences for the planet.
It should be noted that Krutzen was not only an impartial chronicler who showed our harmful effects on nature. He perceived all this much deeper: at conferences, Krutzen often made his plenary speeches not purely scientific, but also partly personal. He showed photographs from his childhood, and then photographs of his grandchildren and said that he was very worried about them: when they were 70 years old, their environment would be much worse than during his childhood. His performances have always made a very strong impression.
Scheme of "planetary boundaries" in the understanding of Krutzen. The safe area is shown in green. The red wedges are the current position estimate for each of the nine variables. Limits for three systems (biodiversity loss, climate change, nitrogen cycle) have already been exceeded
In 2019, Paul Krutzen and Georgy Golitsyn were awarded the main award of the Russian Academy of Sciences - the Lomonosov Grand Gold Medal. For the General Meeting of the Russian Academy of Sciences on the occasion of the awarding held at the end of 2020, Krutzen prepared a lecture entitled “Our grandchildren, like us today, will live in the Anthropocene,” but he could not read it even “by zoom” - his health condition did not allow …
“Our curiosity and desire to understand everything that surrounds us, including ourselves, makes science overturn every stone,” he wrote. "But let's hope that through the acceptance and understanding of our own era, the Anthropocene, … the actions necessary to limit irreversible damage to our planet, especially in the area of global warming effects, have finally received the necessary momentum."